Voltage comparison circuit



y 1954 F. E. TIDBALL VOLTAGE COMPARISON CIRCUIT Filed June 5, 1952 2 Sheets-Sheet l 3 QN Y nu v mm mm i 5 a 4' 3 5L i 5 3 v on N mm 52 on 3 5 on sign 9M ATTORNEY y 1954 F. E. TIDBALL VOLTAGE COMPARISON CIRCUIT 2 Sheets-Sheet 2 Filed June 3, 1952 SAWTOOTH F I62. WAVE CONTROL VOLTAGE GATE VOLTAGE SAWTOOTH FIG 3 WE CONTROL VOLTAGE PULSE GATE VOLTAGE CONTROL VOLTAGE PULSE INVENTOR FRAN K E. TIDBALL BY zjw ATTORNEY Patented July 20, 1954 UNITED STATES 'ATENT OFFICE VOLTAGE COMPARISON CIRCUIT Frank E. Tidball, "Minneapolis, Minn., assignor,

by mesne assignments, to the United States of America as-represented by the Secretary of the Navy 5 Claims.

This invention relates to means for a method of comparing the synchronism of two reoccurring voltages and for providing a control voltage directly proportional to a difference in synchronism of the two voltages. More particularly, the invention relates to a circuit for providing a control voltage proportional to a difference in synchronisin of a gate voltage or" a given frequency and of a sawtooth voltage approximately of the same frequency.

The gate voltage which is a rectangular voltage wave and is to be compared in synchronism with a sawtooth voltage wave is applied to the anodes of a pair of electron tubes. The control electrode in one of these tubes is at ground potential and both electron tubes are cut-01f until the gate voltage in amplified form is applied to the anodes thereof. The control electrode of the other of the electron tubes has the sawtooth voltage applied thereto. The sawtooth voltage wave is so constituted that, at the beginning of each cycle, the voltage rises linearly to a peak at the end of the cycle and then falls almost instantaneously to a negative maximum at the beginning of the cycle. Centrally of the sawtooth voltage wave the voltage is made to pass thrOugh zero potential, at which point the control electrode of the second electron tube is also at ground potential.

A control pulse either positive or negative occurs if the gate voltageapplied to the anodes of the-electron tubes differs in time from the time at which the control electrodes of both electron tubes are at ground potential, at which time the gate voltage is synchronized with the sawtooth voltage. The control pulse for-med by comparing the synchronism of the gate and the sawtooth voltage is negative when the gate deviates to the positive portion of the sawtooth voltage, and is positive when the gate deviates to the negative portion of the sawtooth voltage.

An object of the invention is electronically without moving parts to compare the synchronism of two voltages and provide a control voltage.

.A further object of this invention is to compare the synchronism of two voltages approximately of the same frequency and to provide a control voltage directly proportional to a "difference in synchronism oi the two voltages.

And an additional-object of this invention is to compare the synchronism of a gate and sawtooth voltage and toprovide apulse for forming a control voltage when .the gate deviates from the zero potential of the sawtooth voltage.

The invention as to organization and manner of operation together with further objects and advantages thereof may best be understood by reference to the ffollowing detailed description taken in connection with the accompanying drawing wherein Figure 1 is a circuit diagram showin the electronic elements of the invention in a prefererd embodiment; Figure 2 is a graph of the voltage -time wave shapes of the circuit of Figure 1 when the comparing electron tubes gate in synchronism with the zero potential point of the sawtooth voltage appearing on the control electrode of the second electron tube; Figure 3'is a graph of the voltage-time Wave shapes of the circuit of Figure 1 when the comparing electron tubes gate at-atime when the positive portion of the'sawtooth voltage appears onthe control electrode of the second electron tube; and Figure 4 is "a graph-of the voltage-time wave shapes ofthe circuit of Figure 1 when the comparing electron tubes gate at a time when the-negative portionof the sawtooth wave appears on the control electrode oi the second electron tube. Identical circuit features in each figure havebeen designated with the same numerical identification.

Referring particularly to Figure 1, the electronic circuit comprises a-diode I, the anode 2 of which passes a negative gate voltage 3 to the controlgrid 4-of a first pentode tube 5 which gate voltage is compared in synchronism with --a sawtooth voltage 6 from .a sweep generator I.

The pentode tube 5 having an anode 8 and cathode 9 isop'eratingas .a class A amplifier and is normally conducting, and has an .anode to cathode circuit connected between ground and a source :of positive potential 59 through the anode load resistance In. The screen grid H of pentode 5 is connected to a source of positive potential 5.! and the control grid 4 is connected to the anode 2:O'f di0de l .and through the grid resistor I2 to ground.

The "diode I offers-a low reactance to the negative gate voltage 3 and the-grid resistor 12 is of large value so that-the shunting effect of thegrid resistor I2 is small. During intervals between gating voltage pulses the pentode 5 conducts considerable anode current and the voltage drop across the anode load resistance H] is large. The

negative gate voltage 3 which is applied to the control grid 4 cuts off the pentode tube 5 for the duration of the gate voltage and the anode current of pentode tube 5 drops. The voltage drop across anode load resistance it therefore decreases and the voltage at anode 8 increases to equal the voltage of the source 50.

A pair of electron tubes I3 and M which have anodes l5 and 56 respectively connected to the anode ii of pentode tube 55 comprise the voltage comparison circuit for comparing the synchronism between the gate voltage 3 and the sawtooth voltage 6. The control electrode 11 of electron tube i3 is connected to ground, and the control grid N3 of electron tube it is connected to the sawtooth voltage 6 appearing across cathode resistor I 9 of the tube 20.

The sawtooth generator produces a voltage which increases linearly with time during the cycle from a minimum voltage to a maximum voltage and then decreases almost instantaneously to the minimum voltage to begin a new cycle. This voltage is impressed on the control grid a of the cathode follower tube 20, the anode 28b of the tube 28 being connected to a source of positive voltage 52 and the cathode 26c being connected to a source of negative voltage 53 through the potentiometer i9. Since the source or" negative potential is considerably below ground potential, the cathode 20c may vary over a wide range from below ground potential to above ground potential and a corresponding voltage appears across the potentiometer it, A portion of this voltage is impressed on the grid 58 of tube i l, the proportion being determined by the setting of the potentiometer l9 which acts to vary the point in the cycle of the sawtooth wave at which the voltage on the grid i8 is equal to ground potential. The potentiometer i9 therefore serves as a phasing control for the circuit.

The cathodes 2i and 22 of the electron tubes l3 and iii are connected to ground through the equal cathode resistances 23a and 24, the cathode 2! being connected to the cathode of the tube 21 through the cathode resistance 23b. As will be hereinafter explained in more detail, the current conducted by tube 21 is conducted through resistance 23a and provides a negative bias on the grid H with respect to the cathode 2 i.

The cathode 22 of the tube M is raised to positive potential by means of a source of positive potential by a circuit extending from the source in positive potential 54 through the variable resistance 29 and resistance 26 to ground. The variable resistance 29 is adjusted to make the voltage drop thus produced across the resistance 2 equal to the voltage drop produced across the resistance 23a by the current conducted by tube 27 when the tube 21 is conducting normally, so as to balance the conduction characteristics tubes 13 and 54.

During the time interval between gating voltage pulses, the pentode tube 5 conducts heavily, since its control grid 4 is not biased negative with respect to its cathode, and the current conducted by the pentode tube 5 through the load resistance it produces sufficient voltage drop across the resistance ill to reduce the voltage at the anodes 8, i5 and it to about 25 volts. The cathodes 2i and 22 of the tubes i3 and id are raised above ground potential by the circuit as previously explained sufficiently to prevent conduction of the tubes I3 and Hi. However, when the gate voltage pulse is impressed on the grid l of the pentode 5 to momentarily prevent con-- duction therethrough, the voltage applied to the anodes 5 and it rises sufliciently to render these tubes conductive and therefore responsive to the potentials impressed on their respective grids. If the potentials on the respective grids of tubes l3 and id are equal at the time the gating voltage pulse is impressed on the grid i of tube 5, the conduction of tubes l3 and id are equal as are the voltages on their respective cathodes. However, if the potentials on the grids ll and is with respect to ground are unequal, the tube having the more positive grid potential will conduct more heavily, and its cathode will therefore be raised more positive than the cathode of the other.

The tube 21 is connected to amplify the difference in voltage produced between the cathodes 2i and 23 by any inequality in conduction of the tubes l3 and it. As described herein, the tube 2? is a sharp cut-off pentode to provide high gain and sensitivity, but it will be readily apparent to those skilled in the art that a wide variety of tubes could be employed if desired. As previously mentioned the cathode 2! of tube 53 is connected to the cathode 25 of tube 27 through the resistance 23, the resistance 23 being paralleled by the capacitor 33 which prevents rapid changes in the voltage appearing across the resistance 23b. The suppressor grid 28 is connected to the cathode 25, and the control grid 2% is connected to the cathode 22 of tube it, while the anode is connected to the source of positive potential through the load resistance 35.

The operating characteristic of the pentode tube is affected in large measure by the voltage difierence between its cathode and screen grid, and in the present application the potential of the cathode 25 of tube 27 is periodically raised by an appreciable amount of application of a gate voltage pulse to the pentode 5. In order to stabilize the operation of tube 2i, the voltage impressed on its screen grid 39 relative to its cathode 25 is maintained substantially constant by means of the series dropping resistance 3! connecting the source of positive potential at to the screen grid 38 and the neon regulator tube 32 connected between the screen grid as and the cathode 25.

The operation of the voltage regulator circuit comprising the dropping resistance E i and the neon regulator tube 32 is conventional. When the voltage impressed on the tube 2-32 increases, the current conducted by the tube increases and thereby increases the voltage drop produced across the resistance 3i to reduce the potential impressed on the screen grid 3%. A voltage decrease will produce an opposite action.

The output voltage of the anode 35 of tube 2? is impressed through coupling resistances 39 and ill on the resistances ii and ii. respectively, so that equal pulsating voltages appear across the resistances ii and ,2. The positive pulsations of the voltage appearing across the resistance ii are rectified by the diode 31, while negative pulsations appearing across the resistance 32 are rectified by the diode 38, and since the pulsations as hereinafter explained occur in only one direction at a particular instant, the output diodes 37 and 38 is a direct current voltage having a polarity magnitude determined by the magnitude and polarity of the potential difierence between the cathodes 2i and 22 at the instant the gate voltage pulse is impressed on the pentode 5.

A positive pulse forms when the electron tubes I 3 and "is are gated and the control grid it of the electron tube it is negative, 1. e., the electron tubes is and it are gated during the negative portion or the sawtooth voltage 6. A negative pulse voltage forms when the electrode tubes l3 and It are gated and the control electrode of the electron tube H5 is positive, 1. e., the electron tubes 53 and it are gated'during the positive portion of the sawtooth voltage 6.

A storage network or filter 4 3 from the lead 41 connected with the diodes 3? and 38 respectively to ground provides smoothing to the control voltage when a positive or negative pulse is passed by the valve 3? or 38 indicating that the gate voltage 53 not synchronized with the zero potential point of the sawtooth voltage 6. Typically filter it may be a large capacity condenser capable of retaining considerable energy.

The gate voltage 3 is shown in each of Figures 2, 3, and 4 which illustrate graphically the changes in circuit conditions when the electron tubes is and [4 are gated. The gate voltage 3 is shown as function of time and reoccurs at approximately the time intervals. Beginning at zero time, the sawtooth voltage 6 is also illustrated as a reoccuring voltage of the same frequency as gate voltage 3. When these voltages are synchronized, the control voltage of curve a of 2 appears at the anode 35 of the tube The condition whereby the electron tubes and i i are gated at a time at which the control g d it or the electron tube it is at a positive potential is illustrated in Figure 3, and the negative voltage pulse illustrated in curve b appears at the anode 35 of the pentode El: likewise the condition whereby the electron tubes is and i i are gated at a time at which the control grid it of the electron tube is is at a negative potential is illustrated in Figure 4, and the positive voltage pulse illustrated in curve appears at the anode 35 of the pentode 2?.

The circuit of Figure l operates to provide a positive or negative voltage pulse directly proportional to the difference in synchronism of the gate voltage 3 pulse indicated by and the sawtooth voltage 5. The electron tubes is and M compare the synchronism of the two wave indi cated by voltages and the control grid-to-cathode circuit or the tube 2'1 changes potential if a difference in synchronisrn exists. The change of potential in the control grid-to-cathode circuit of tube 2? change the conductivity of the tube 21. The control grid-to-cathode voltage of the tube 21 is stabilized during the interval between gating voltage pulse.

The control grid ll of electron tube It is at ground potential and the control grid it of electron tube it is at ground positive, or negative potential dependent upon the phase and synchronism of the sawtooth voltage wave 6 and the gate voltage wave 3.

It is of course to be understood that the voltage pulse from the anode 35 of the tube 27! may be used directly or filtered by a filter 48 to provide a direct current control voltage for synchronizing the gate voltage wave and the sawtooth voltage wave 6, and that ordinarily only a small portion of the gate voltage 3 is needed to provide the voltage pulses used to provide a synchronous condition.

While a particular embodiment of the invention has been illustrated and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects.

For example, the voltage pulses or control voltage maybe applied to control an oscillator frequency, a motor speed, orother device, and it is therefore an aim in the appended claims to cover all such changes and modification as fall within the true spirit and scope of this invention.

What is claimed as new is:

:1. A circuit for comparing the synchronism of two reoccurring voltages of approximately the same frequency to provide a voltage directly proportional to a-diiference in synchronism of said voltages comprising, in combination, a normally conducting electron tube having an anode, control electrode and cathode, an anode resistor connected to said anode of said normally conducting electron tube and to a source of anode voltage, whereby conduction of said normally conducting electron tube reduces the anode voltage thereof, a source of sawtooth voltage having a zero potential point centrally of the sawtooth, a first and second electron tubes each having an anode, a cathode, and a control grid, said anodes being connected in parallel with the anode of said normally conducting electron tube and said control grids being connected respectively to zero potential and to said sawtooth voltage, means connected to the cathodes or" said first and second electron tubes for normally biasing said first and second electron tubes to cut-off, a gate voltage, means for applying said gate voltage to said normally conducting electron tube thereby to raise the anode voltage of said paralleled anodes for the duration of said gate voltage to render conductive said first and second electron tubes, and current comparing means for measuring the difference in conduction of said first and second electron tubes and for providing a control voltage proportional to said difierence in conduction.

2. The circuit of claim 1 in which the current comparing means comprises a pcntode tube having a stabilized screen grid-to-cathode voltage and a control grid-to-cathode circuit connected to said first and second electron tubes to receive a voltage therefrom proportional to the difierence in conduction of said first and second electron tubes during the conduction thereof.

8. The circuit of claim 1 in which the current comparing means comprises a third electron tube having a cathode and a control grid connected to the respective cathodes of said first and second electron tubes, whereby the conduction of said third electron tube varies with the difference in conduction between said first and second electron tubes.

4. A circuit for comparing the synchronism of a source of rectangular voltage and a source of sawtooth voltage comprising a first and a second electron tube each having at least an anode, a cathode and a control grid, means connecting the anodes of said first and second electron tubes to each other and to an anode resistor, means connecting said anode resistor to a source of anode power, individualized resistor means connecting said cathodes of said first and second electron tubes to ground, a normally conducting electron tube having its anode connected to the anodes of said first and second electron tubes whereby conduction of said normally conducting electron tube reduces the anode voltage of said first and second electron tubes, means connecting the control grids of said first and second electron tubes to ground and to the source of sawtooth voltage respectively, means impressing the voltage from the rectangular voltage source on said normally conducting electron tube to render it non-conductive thereby to render said first and second electron tubes conductive, and comparison means connected to the respective cathodes of said first and second electron tubes to produce a voltage proportional to the difierence between the conduction of said first and second electron tubes.

5. The circuit as claimed in claim 4 wherein said comparison means comprises a third electron tube having a cathode and a control grid connected to respective ones of the cathodes of said first and second electron tubes, whereby the conduction of said third electron tube varies with the difference in conduction between said first and second electron tubes.

References Cited in the file of this patent UNITED STATES PATENTS 

